Use of atomizer nozzles is known in the art as illustrated in U.S. Pat. Nos. 5,547,368, 5,567,141, 5,393,220 and 5,617,997, incorporated herein by reference in their entirities. As described in U.S. Pat. No. 5,547,368, atomizer nozzles are used in industrial melting furnaces for such diverse products as metals, glass, ceramic materials, and the like.
There are many ways of atomizing liquid fuels in combustion applications. The nozzles can be grouped in two major groups:                a) Pressure atomizers, where relatively high liquid fuel pressure is used to drive the flow through a small orifice, which breaks up the liquid into droplets. These atomizers are relatively simple. However, their turn down ratio is narrow requiring nozzle changes for systems that have wide variations in flow requirements.        b) Twin-fluid atomizers, where an atomizing gas is used to assist with liquid atomization. The atomizing gas usually is introduced at higher pressures, while the liquid fuel may be delivered at lower pressures. This group of nozzles can further be segmented into:                    1) External-mixing, where the high-velocity atomizing gas meets with lower-velocity liquid fuel externally resulting in liquid-jet breakup, i.e. atomization. These nozzles are usually very rugged, however, the flame shape and atomization quality is most-often sub-optimal, especially in oxy-fuel burner applications. The flames are short, tight, leading to non-uniform heat delivery and local overheating.            2) Internal-mixing or emulsion, where the atomizing gas and liquid fuel are mixed inside an internal chamber, and the two-phase mixture is then ejected through an exit orifice causing liquid breakup due to depressurization of inter-mixed gaseous phase. These nozzles produce excellent and controllable atomization, excellent flame geometry and uniform heat transfer.                        
While the internal-mixing atomizers are widely used in air-fuel combustion, their use in oxy-fuel burners have been limited due to cooling concerns and possible flame flash-back issues. With non-water-cooled burners, the primary oxidizer cools the atomizing nozzle. For air-fuel burners in which the primary oxidizer is air cooling is accomplished due to the large volume of air (the primary oxidizer) that is needed and provided for complete combustion. However, for oxy-fuel burners, which are burners utilizing a primary oxidizer with a higher O2 concentration than air, cooling of the atomizing nozzle via the reduced volume of the primary oxidizer may be unsatisfactory. For example, in case of a 100% O2 oxidizer, if the stoichiometric required amount of oxygen for combustion is provided, there will be about 80% less volume of the primary oxidizer available to cool the atomizing nozzle than in air-fuel burners. In addition, oxy-fuel burners have much higher flame temperatures. For these reasons the atomizing nozzles in oxy-fuel burners are expected to run at much higher temperatures than in air-fuel burners.
Higher internal-mixing nozzle temperatures lead to several potential problems:                1) Elevated nozzle temperatures may cause chemical degradation of liquid fuels prior to their introduction into the furnace. More specifically, for fuel oils, such as heavy oils with high sulfur content, and oils with high carbon residue values (CCR) (e.g. oils with high levels of asphaltenes), high nozzle temperatures may lead to internal coke deposition and nozzle plugging. This is a concern regardless of the atomizing gas used.        2) Additionally, if oxygen is used as the atomizing gas, elevated nozzle temperatures and improper nozzle design may lead to flame flash-back and a catastrophic nozzle failure or meltdown.        
The present invention teaches how to avoid the above operating problems by proper nozzle design.